2011

Move from HIGH to LOW concentration-“passive transport”

-no energy needed

diffusion osmosis

movement of water

Diffusion through protein channels◦ channels move specific molecules across

cell membrane

◦ no energy needed

“The Bouncer”

open channel = fast transport

facilitated = with help

HIGH

LOW

Cells may need to move molecules againstconcentration gradient-conformational shape change transports solute from

one side of membrane to other -protein “pump”-“costs” energy = ATP conformational change

ATP

LOW

HIGH

symportantiport

Many models & mechanisms

ATP ATP

Membrane potentialthe voltage difference across a membrane

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Electrochemical gradientcaused by the concentration electrical gradient of ions across a membrane

Electrogenic pumpa transport protein that generates the voltage across a membrane

CotransportOccurs when active transport of a

specific solute indirectly drives the active transport of another solute

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Involves transport by a membrane protein

Driven by a concentration gradient

Where else have you seen this concept?

Cotransport: active transport driven by a concentration gradient

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Where else have you seen this?

Passive TransportSimple diffusion

diffusion of nonpolar, hydrophobic moleculeslipids

HIGH LOW concentration gradient

Facilitated transport diffusion of polar, hydrophilic molecules

through a protein channel

HIGH LOW concentration gradient

Active transportdiffusion against concentration gradient

LOW HIGH

uses a protein pumprequires ATP ATP

simplediffusion

facilitated

diffusion

active

transport

ATP

Bulk transport across the plasma membrane occurs by:

exocytosis and endocytosisLarge proteins

Cross the membrane by different mechanisms

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How about large molecules?

Movement into & out of cell-through vesicles & vacuoles

Endocytosis: in phagocytosis = “cellular eating” pinocytosis = “cellular drinking” Recepter-mediated

Exocytosis: out

exocytosis

In exocytosisTransport vesicles migrate to the plasma membrane, fuse with it, and release their contents

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In endocytosisThe cell takes in macromolecules by forming new vesicles from the plasma membrane

http://www.youtube.com/watch?v=npYUjxWrhfo

http://www.youtube.com/watch?v=aWItglvTiLc&feature=related

http://www.youtube.com/watch?v=KxTYyNEbVU4&feature=related

forms new vesicles from the plasma membrane

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phagocytosis

pinocytosis

Receptor-mediated

Endocytosis

(1) phagocytosis: “cellular eating”

cell engulfs a particle: extends pseudopodia around it & packages it in a large vacuole.

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http://www.youtube.com/watch?

v=aWItglvTiLc&feature=related

http://www.youtube.com/watch?v=U9pvm_4-bHg

http://www.youtube.com/watch?v=JnlULOjUhSQ&feature=related

http://www.youtube.com/watch?v=JnlULOjUhSQ&feature=related

http://www.youtube.com/watch?v=pvOz4V699gk

http://www.youtube.com/watch?v=aWItglvTiLc&feature=related

(2) pinocytosis: “cellular drinking”

cell creates a vesicle around a droplet of extracellular fluid(non-specific process)

http://www.youtube.com/watch?v=v8XaY-

vVtcA&feature=results_main&playnext=1&list=PLF8E2635BAFF54082

(3) Receptor-mediated: very specifictriggered when extracellular substances bind to

receptors/ligands on the membrane surface, especially near coated pits

triggers formation of a vesicle